Ambartsumian’s Knot is a dwarf elliptical galaxy in the constellation Ursa Major. It is the small blue dot off the bottom of the eliptical NGC3561A.[2]

The entire system is called Arp 105, or “The Guitar”, because of its overall shape. “The Guitar” as an example of new galaxies being formed as ejections from older galaxies.[4][1]

Ambartsumian’s Knot is located at the end of what appears to be a bridge of matter extending from the elliptical galaxy NGC 3561B (R.A. 11h 11m, Dec. +28° 42′). The latter is interacting with the nearby spiral galaxy NGC 3651A giving rise to a number of tidal tails and tidal dwarf galaxies. [2][3][4]

The enormously long tidal tail visible to the left (north) of NGC 3651A in the accompanying photo, Arp 105N, stretches out for 100,000 parsecs (325,000 light-years) from the parent galaxy.[2]

Arp 150 lies close to the center of the rich cluster Abell 1185, which lies about 400 million light-years away. [2]